Updated 5:37 p.m. | President Barack Obama would veto an emerging $450 billion tax cut deal coming together in the Senate because it doesn't do enough for the middle class, according to the White House.

"The President would veto the proposed deal because it would provide permanent tax breaks to help well-connected corporations while neglecting working families," said Jen Friedman, deputy White House press secretary.

The emerging package of tax cuts negotiated by top Democrats and Republicans would extend an array of mostly business tax breaks — some permanently — while some of the president's priorities would be left on the cutting room floor.

The package includes the research and development break and is expected to revive a slew of other provisions that benefit corporate interests, including NASCAR, film producers and the owners of racehorses.

The so-called "tax extenders" package has been in the works for months, after most of the provisions expired in January. Democrats negotiated to add some of their preferred tax cuts, including a tax subsidy for mass transit and the deductibility of sales taxes, but other provisions, like an enhanced Earned Income Tax Credit, would expire. The roughly $450 billion pricetag over a decade would add to the deficit. Outside deficit watchdogs warn that would effectively change the baseline for any future tax reform.

The additional red ink would also knock House Budget Chairman Paul Ryan's budget blueprint out of balance in the 10th year — meaning Republicans would have to find other cuts to make or raise revenue elsewhere if they still wanted to eliminate future red ink.

It would also turn Ways and Means Chairman Dave Camp's own tax reform plan into a $450 billion tax increase and presumably a violation of Americans for Tax Reform's pledge — signed by most Republicans — not to raise taxes.

With the backing of senior Senate Democrats, it's conceivable the Senate could have the votes to override a veto on a tax cut package. In that case, House Minority Leader Nancy Pelosi, D-Calif., could end up being the presidential veto backstop, if it comes to that.

One of her lieutenants, Rep. Chris Van Hollen, D-Md., ripped the deal Tuesday.

"The package would provide a permanent boon to large corporations, even those that renounce their U.S. citizenship and invert," he said. "And adding insult to injury, the proposed deal chooses to leave behind working families and would make things harder for millions of Americans. ...The overall package is simply unacceptable and adds more than $400 billion to the debt. We need to grow the middle class, not punish those working hard to get by while always giving preferences and priority treatment to big corporations who can hire high-priced, well-funded lobbyists."